Overview

Cable modem technology is similar to DSL in that it is unique to the underlying technology infrastructure, which in this case is a hybrid-fibre coaxial cable system designed for the primary purpose of delivering video signals. CATV or cable television systems were first deployed in the U.S. in the late 1940s for the transmission of broadcast television services in areas that were unable to receive broadcast signals, as the result of distance or terrain.[xxii]  The earliest deployments of commercial cable television systems were in the U.S. and Canada, which have among the highest penetration rates in the world.

Both the U.S and Canada are unique among OECD countries, in that cable modems still dominate the high-speed Internet access market.  This has been the result of a number of factors, including the high penetration rate of cable in these countries, the major capital investments made by the industry to upgrade its cable television plant to provide two-way capability, the availability of a reliable cable modem technology, and the early recognition of an emerging market opportunity for high-speed Internet access. Although Bellcore first pioneered DSL technology in the 1980s, telephone companies were reluctant to deploy this technology and did not do so until cable modems represented a significant competitive threat to their existing dial-up Internet business.

Cable television systems were initially designed as one-way systems that delivered analogue television signals to their customers through a coaxial cable network using a node and branch structure.  In order to meet the demands for increased television channels and interactive services, like pay-per-view, cable operators have had to make major capital expenditures to upgrade their systems to increase channel capacity and provide two-way capability.

Cable modems can provide high-speed access to the Internet, particularly in the download segment where transmission speeds can be in excess of a T1 or E1 circuit. In modern cable systems with two-way capability, television services and Internet access are provided to the customer’s premise through a cable, which in turn is divided into two connections by means of a splitter.  One of the connections goes either to the television or a set-top box and provides broadcast services, while the other connects to a cable modem to provide Internet access. 

The cable modem is connected to either an Ethernet network card installed within the computer or by means of a universal serial bus (USB), which makes the installation process much easier and faster.  These are then configured with the use of software to enable the computer to connect and interact with the Internet.  The uploading and downloading of data between the computer and the Internet are transmitted through the cable lines and controlled by the cable modem and the network card or USB.  The signals delivered to the cable modem are carried on a 6MHz channel within the broadband distribution system.

Cable systems are generally designed with a system of network architecture that divides the serving territory into a series of nodes or local area networks designed to serve 500 or more residences.  This type of network architecture can have an effect on the speed of the cable modem, as all the residences within that node that subscribe to the cable modem service share the available spectrum.  In the U.S., the cable industry has adopted an industry standard for the amount of bandwidth that is available for shared use within a node, about 27 Mbps downstream and 10 Mbps upstream.  Often there are also restrictions on the downstream and upstream transmission speed available to each user to ensure that overall performance levels can be maintained.  However, as the number of subscribers to cable modem services increase, the cable company will often have to decrease the density of nodes by splitting and building new nodes to ensure that an acceptable transmission speed is maintained.

There is also an issue related to the distance that a broadband signal can be delivered from the node and the impact that this has on the quality of the data transmission.  An optimal distance is 2000 feet, but it can be extended to a maximum of 16,000 feet with the use of amplifiers, however, the amplifiers can distort the signal.

The nodes are in turn connected to the cable television head end, which provides both television and Internet services to the subscribers within the nodes.  The head end is also connected to the Internet and its own high-speed Internet servers.  These servers generally include a mail, a newsgroup, and a proxy server. 

Today's cable networks generally deliver data with download speeds roughly between 500 kbps and 3 Mbps and upstream speeds of 128 - 256 kbps. Newer-generation cable-modem technologies have enabled cable operators to provide greater bandwidth service offerings.

Advantages and Limitations

What are the capabilities and advantages of using cable modem technologies?

• Cable modems are independent of telephone lines and so they do not tie up the phone line and like DSL, cable modems can provide continuous access to the Internet.
• Cable modems provide similar service performance capabilities as DSL and the pricing is usually equivalent. 

What are the constraints and disadvantages of using cable modem technologies?

• Cable modem service is shared among multiple users, which can have an impact on the speed of the broadband connection depending on the number of people that are using the service at the same time.
  
• Cable service has not been as universally deployed as telephone service, so it is a technology that is often not available in many areas.
  
• Cable modem services are provided on hybrid fibre-coaxial (HFC) systems.  Given that the cost of constructing a HFC system is similar to that of an all fibre system, it makes more sense to build an FTTH system.

Cable Modem Technology and Local Open Access Networks

The development of cable systems in other countries tended to occur later than North America and for the most part have never reached the level of penetration that exists in North America, particularly with the emergence of competing technologies, such as satellite.  It is unlikely that with the convergence of technology, HFC systems will develop as standalone networks in countries that currently do not have them.  It is more likely that in many countries these services will be provided on existing networks using enhanced DSL technology or on new networks designed specifically for triple play services, such as fibre.

Hybrid Fibre-Coaxial networks are capable of providing local open access, but the cable industry has been opposed to providing access to competitors and is unlikely to do so in the absence of regulations requiring them to do so.  The issue is not one of technology, but rather the business model adopted by the cable industry.

 
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